1. Field of the Invention
The present invention relates to a fiber channel arbitrated loop (generally abbreviated to FC-LA) technology, and more particularly to a technology for avoiding system breakdown, when a component failure occurs in an information storage apparatus, such as a magnetic disk apparatus, on a FC-AL configuration, by disconnecting the relevant apparatus from the loop-like transmission path.
2. Description of the Related Art
FC-AL technology has been increasingly utilized for realizing a high speed interface between an information storage apparatus, such as a magnetic disk apparatus, or the like and a host computer. FC-AL technology is a technology which enables high speed data transfer to be carried out by serially transferring data without giving rise to any skew between different data.
In order for a reader to better understand problems associated with a system using conventional FC-AL technology, the construction of a system using conventional FC-AL technology will be described below with reference to FIG. 1 that will be described in the section, “BRIEF DESCRIPTION OF THE DRAWINGS”.
In FIG. 1, a schematic view depicting the construction of a system using FC-AL technology is shown.
As shown in FIG. 1, a host computer 2 and a plurality of magnetic disk apparatuses 3 are connected to the transmission line loop 1. The host computer is not limited to a single unit, and multiple units may be connected.
The host computer 2 and each of the magnetic disk apparatuses 3 are connected to the loop 1 via ports 6. Each of the ports 6 is provided with a driver 4 and a receiver 5. Each apparatus is connected in the form of a loop with its driver 4 connected to the receiver 5 of the port 6 of the apparatus in the following stage. Although, for the sake of simplicity, only one port is provided in each apparatus of the system shown in the Figure, a plurality of ports may be provided in an apparatus so as to form a plurality of loops.
Corresponding to each port, a by-pass circuit 7 is additionally provided. Depending on a control signal (loop enable signal) transmitted from a hard disk controller (HDC) (not shown) of the magnetic disk apparatus, each by-pass circuit 7 selects either the signal transferred from the apparatus in the preceding stage or a signal output from its own driver 4 as the signal to be sent out to the apparatus in the following stage. The loop enable signal is transmitted to the by-pass circuit 7 through a dedicated signal line 8. When a failure occurs in a magnetic disk apparatus 3, the HDC of the relevant magnetic disk apparatus 3 detects it and cancels the loop enable signal accordingly. In response to this cancellation of the loop enable signal, the by-pass circuit 7 selects the signal input from the apparatus in the preceding stage, and the magnetic disk apparatus 3 in which the failure occurs is thereby by-passed.
As has been described above, transmission of the control signal to the by-pass circuit 7 at the time of occurrence of a failure is performed by the HDC. However, when trouble occurs in a reference clock generator or a power supply, the HDC itself cannot function normally. In this case, the loop enable signal is not properly sent out so that the failed magnetic disk apparatus remains on the loop. In such a state, unexpected data are transferred to other magnetic disk apparatuses connected to the loop, leading to a breakdown of the loop.